Conventionally, a scan correlation in which an echo level is adjusted by using statistical processing based on a latest echo and also a previously acquired echo, so as to create a radar image, is known. By performing the scan correlation, although an echo of a water surface reflection can be suppressed, an echo of, for example, a ship traveling at high speed is also suppressed. Therefore, the scan correlation is preferably performed with suitable processing contents per processing target.
JP3680265B discloses an art in which an area is divided into an interior region and an exterior region, and the processing contents of the scan correlation are differentiated therebetween. Specifically, since a water surface reflection tends to occur at close distance, in the interior region, the scan correlation is performed to increase an influence of a previously acquired echo. Further, in the exterior region, the scan correlation is performed to increase an influence of a latest echo. In this manner, an influence on a target object can be reduced while suppressing the water surface reflection.
JP2006-112973A discloses an art in which whether an echo exists is detected in every pixel in an image memory, and unstableness is detected in every pixel based on a number of times the result of whether the echo exists varies in a plurality of previous scans. For the pixel with high unstableness, the water surface reflection is considered to have occurred, and a scan correlation is performed to increase an influence of a previously acquired echo. Further, JP2009-058433A discloses an art in which not only a pixel with high unstableness, but also pixels therearound are considered unstable and a scan correlation is performed thereon. Thus, a water surface reflection is accurately suppressed.
Meanwhile, there is a case where the echo suppression is not necessary even when the unstableness of the echo is high. For example, for fishing gears (float, flag buoy, etc.) installed in water, since they sway due to occurrence of waves, wind, etc., the number of times the result of whether the echo exists varies easily becomes large. Therefore, with the radar apparatuses of JP2006-112973A and JP2009-058433A, areas where these fishing gears are installed are considered unstable, and echoes of the fishing gears etc. may be suppressed.
However, the echoes indicating locations of the fishing gears are necessary for an installer of the fishing gears, and it is not suitable to suppress the echoes. Even for people other than the installer, the echoes indicating locations of the fishing gears are necessary in order to avoid the fishing gears in navigation.